MODELLING AND MANAGING 3D SPATIAL OBJECTS. Siti Nur Awanis Mohamad Zulkifli and Alias Abdul Rahman

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1 MODELLING AND MANAGING 3D SPATIAL OBJECTS Siti Nur Awanis Mohamad Zulkifli and Alias Abdul Rahman Departments of Geoinformatics, Faculty of Geoinformation Engineering and Sciences, Universiti Teknologi Malaysia, UTM Skudai, Johor, Malaysia utm.my Abstract Currently, variety of software is already capable of handling a wide range of spatial problems, beginning with approaches for describing spatial objects to quite complex analysis and 3D visualisation. However, increasing number of applications need more advanced tools for representing and analyzing the 3D world. Among all types of systems dealing with spatial information, GIS has proven to be the most sophisticated system that operates with the largest scope of objects (spatial and semantic), relationships and provide means to analyze them. However, how about 3D GIS? It is the aim of this paper to find the answer by analyzing the available software. A 3D case study performed in Oracle Spatial and MicroStation Bentley Map provides knowledge about the 3D functionality offered by commercial systems. At the end, the paper addresses some of the issues and problems involved in developing such a system and recommends directions for further research. Key Words: 3D Spatial Objects, DBMS 1.0 INTRODUCTION Nowadays, GIS users are getting more complex datasets and needs to manipulate and generate information as we perceived in the real world, i.e. in 3D environment. This environment provides better understanding of geospatial pattern and phenomena either in small or large areas. Relevant questions such as: How we model the real world object, i.e. 2D and 3D spatial objects in DBMS and visualizing the objects in GIS/CAD frontend? Answering this question provides on interesting experiment toward realizing 3D geospatial database. In general, many organisations realize the needs for a central DBMS: a system that spatial and attribute data are maintained in one integrated environment. Many DBMSs are capable of maintaining spatial data in 2D, since spatial data types and data structure in 2D have been implemented in DBMSs. However, aspect of 3D data still needs a lot of efforts to be addressed. Over the last few years we have seen an increasing amount of work in the field of modeling and managing 3D spatial objects. A number of projects were focusing on the modeling and management of complex 3D objects in a primarily relational DBMS environment, e.g. (Pfund, 2001), (Wang, 2000). Some ongoing projects employ object-relational concepts to address the issues of topology (Oosterom et al., 2002) and integrated 3D geodata management within a 3D GIS framework, e.g. (Nebiker, 2002a), (Zlatanova et al., 2002). Therefore, in this paper we highlighted all the experiment to manage and modelling 3D spatial objects using Oracle Spatial and Bentley Map. Section 2 elaborates the method on how to represent the 2D and 3D spatial objects in the DBMS. In section 3, the experiment on managing the 3D spatial objects are highlighted. Finally, section 4 concludes all the current work. 2.0 MODELLING THE REAL WORLD OBJECTS The real world objects can be described into two components, i.e. 2D objects such as lot parcels and 3D objects (e.g. buildings). Real world objects are characterized based on certain representation and storage within the DBMS. The representation depends on the purpose of the application of the database, identification and data capture process.

2 2.1 2D Objects In general, 2D objects could be represented by a series of polygon geometry, and their nodes as list of points i.e. connected one-by-one by straight line segments and the last point connected to the first. For example, 2D lot parcels in 2D DBMS are mostly represented by closed polygons, as this will simplify objects identification in GIS. Most lot parcels are identified and captured as a closed polygon as shown at figure D Objects Figure 1: 2D object by closed polygon The representation of real world objects is far more complicated when we move to 3D application. In 3D, opposed to 2.5D, it is not possible to assume that objects can be flattened and defined as polygon footprint on the surface. Instead, a proper 3D model representation of the object is needed, meaning more than one Z-value is attached to a 2D polygon and more information is needed than one Z-value attached to the vertices of the 2D polygon (Zlatanova, 2000). In 3D, the definition of the geometrical and topological description and validation of the correctness is far more complicated than in 2D. The polyhedral approach, as described in among others (Stoter, 2004) defines the polygons, where each polygon should be flat and valid according to the Simple Feature Specification (SFS) of the Open Geospatial Consortium (OGC), i.e. non-self intersecting. The set of faces should enclose a single volume. For example, in this research Oracle Spatial 10g are used to manage 3D points, lines and polygons. Using 3D polygons, 3D spatial objects can be represented as polyhedron in two methods: face-by-face polygons. multipolygon collection. In the first method, 3D objects are defined as face-by-face polygons. This model is partly a topological model; since the body is defined by references to the faces (faces share two bodies). To develop 3D objects, series of coordinates that contain x, y, z are extracted from one face of object to another face of object. The 3D object was stored as a list of 3D polygon and it defined by reference to the faces and the faces can be shared by neighbour-bodies as shown at Figure 2. The generated tables for stored 3D object face-by-face look as shown in Table 1. (a) (b) (c)

3 Figure 2: The extracted coordinates (face by face) of the 3D object, (a) Build_ID: 1, (b) Face_ID: 1, (c) list of coordinate for face 1. Table 1: Coordinates list face by face Build_ID Face_ID Shape(mdsys.sdo_geometry) 1 1 x1,y1,z1 x3,y3,z3 x4,y4,z4 x2,y2,z2 x1,y1,z1 2 x7,y7,z7 x1,y1,z1 x2,y2,z2 x5,y5,z5 x7,y7,z7 3 x2,y2,z2 x4,y4,z4 x6,y6,z6 x5,y5,z5 x2,y2,z2 4 x7,y7,z7 x8,y8,z8 x6,y6,z6 z5,y5,z5 x7,y7,z7 5 x1,y1,z1 x3,y3,z3 x8,y8,z8 z7,y7,z7 x1,y1,z1 6 x8,y8,z8 x3,y3,z3 x4,y4,z4 z6,y6,z6 x8,y8,z8 An advantage of face by face polygons is that it is recognized as one object by front-end applications (GIS/CAD) that can access, visualize, and edit these data and post the changes back to the database so we can easily store the information about the object i.e. face 1 represent the wall and face 2 represent the roof. In second method defining 3D object using multipolygon collection method, a 3D object is stored as one record instead of a set of records. The multipolygon, which is also supported in Oracle Spatial, is used for this representation. This has also been implemented and the example to store 3D objects using multipolygon method as shown in Figure 3. Figure 3: Representation of 3D object using multipolygon method. An advantage of 3D multipolygons (compare to face by face polygons) is that it is recognized as one object by front-end applications (GIS/CAD) that can access, visualize, and edit these data and post the changes back to the database. Another advantage of the 3D multipolygon approach is the one-to-one correspondence between a record and an object. 3.0 MANAGING 3D SPATIAL OBJECTS Over the last few years we have seen an increasing amount of work in the field of modeling and managing geospatial 3D objects. A number of projects were focusing on the modeling and management of 3D objects. 3.1 Study Area The study area in this research is Suleymaniye, Istanbul, Turkey. In this area, we assume the following scenario: the user has 3D data organized only in a database (a quite common case for real world data), i.e. no file with graphical information (e.g. DGN) exists. We have experimented with a set of buildings from the Suleymaniye area. Planar rectangular faces constitute each building. The data are build in CAD and further

4 converted to the geometry representation of Oracle Spatial 10g. The conversion is completed with a topologygeometry of the 2D and 3D spatial object. Since the Oracle Spatial 10g geometry does not maintain a true 3D object, we represented every building as a set of faces (walls, flat roofs and foundations). The faces are stored as polygons with 3D coordinates. In this experiment table LOT stored 2D object, table BUILDING represent 3D object stored face by face and table BODY_BUILDING stored the whole 3D object as a one object. Figure 4 shows the Suleymaniye area. 3.2 The conceptual data model Figure 4: Satellite image of the Suleymaniye (Source: Goggle Earth, 2008) In general, the conceptual data model is the basic contents for organize spatial and attributes data. The conceptual model is a core of spatial data model design, which is used to define some rules for representing attributes of spatial model. The main entities in managing the 3D spatial objects for Suleymaniye area consist of LOT, ROAD, PARCELLER, BODY_BUILDING and BUILDING. Figure 5 shows ER-Diagram for modelling Suleymaniye Area.

5 Figure5: ER Diagram of Suleymaniye Area In this model, the 3D objects were represented by BODY_BUILDING and BUILDING tables. All of these tables contain geometry and attributes of the objects. The attribute components for the 3D objects No_Lot: number of lot parcel Build_Name: name of the building Build_ID: Id of the building Age: age of the building Face_ID: Id of the faces Material: Material of the faces e.g. brick, concrete Description: Description of the faces e.g. wall, roof The geometry components for the 3D objects Polygon: include the geometry of the object The components of 2D objects consist of LOT, PARCELLER and ROAD. The attributes and geometry for 2D objects components are as follows: The attributes for 2D objects No_Lot: number of lot parcel Lot_Perimeter: perimeter of the lot Lot_Area: area of lot P_Perimeter: perimeter of the parcel Parcel_Area: area of the parcel Parcel_ID: ID of the parcel Road_ID: ID of the Road Road_Name: name of the road Length: length of the road Width: width of the road Type: type of the road e.g. highway

6 The geometry component for 2D objects Polygon: include the geometry of the object 3.3 The logical model In this experiment two tables that represent 3D objects are develop as shown in Table 2. In the table, BODY_BUILDING the 3D spatial object is defined by a set of records. This table was constructed by using multipolygon method. In the table BUILDING, the actual geometries of faces are stored as face-byface method. Table 2: Description of BODY_BUILDING and BUILDING table. 3.4 Storing of 3D object using face-by-face method The 3D objects in table BUILDING are stored using face-by-face method and the example to store the 3D object in Oracle as shown at Figure 6. Figure 6: The 3D Face store by faces 3.5 Storing of 3D object using multipolygon method In the table BODY_BUILDING, the 3D objects are stored by multipolygon method and the example to store the 3D objects in Oracle as shown in figure 7.

7 3.6 Managing 2D and 3D spatial object in DBMS Figure 7: Store 3D object by multipolygon method In managing 2D and 3D spatial object, Oracle Spatial supports storage for 3D points, lines and polygons. In this experiment, we divide into four steps to store spatial object in DBMS. The first step is creating 2D and 3D tables. In this case, we choose the table LOT to represent 2D objects and the table BUILDING to represent 3D objects. The steps to created table for spatial objects as shown in Figure 8. Figure 8: Step 1- creating table in Oracle Spatial The next steps are inserting the dataset. In Figure 9 represent the SQL- how to insert the 2D and 3D datasets.

8 Figure 9: Step 2 - Insert 2D and 3D data. The third step is inserting the metadata. Besides the tables that represent the geometries of the objects, metadata is maintained in Oracle by describing the dimension, lower and upper bounds and tolerance in each dimension. In the following figure (Figure 10), the information on the tables (LOT and BUILDING) is inserted in the metadata table. The final step, a spatial index (r-tree in 2D and in 3D) is created in the tables (to speed up spatial queries) as shown in Figure 11. Figure 10: Step 3 - Insert the metadata

9 Figure 11: Step 4 - Creating Index. 3.7 The Linkage between Oracle Spatial and Bentley Map Bentley Map is directly integrated with MicroStation and takes advantage of its features i.e. capture, editing, display, and output capabilities. It supported geospatial modelling and interoperability. It also capable to import n export to ESRI SHP files, MapInfo TAB files, Oracle Spatial features and others. In Bentley Map, topological relationships are stored in the DGN file according to the same model employed by Oracle Spatial. This allows complex analysis operations to occur quickly and maintains compatibility with Oracle Spatial for organizations that choose to use Bentley Map as an editing application for Oracle Spatial. The object that we store in Oracle will be appearing when we connect the Bentley Map with Oracle Spatial. Figure 12 and shows the 2D objects and 3D objects were upload into the Bentley Map. 3.8 Editing 3D objects in Bentley Map Figure 12: 2D and 3D model was uploaded to Bentley Map In Bentley Map, we also can edit the spatial objects using the EDIT function. After editing, we can post the new object directly to Oracle database as shown in the figure 13.

10 Figure 13: Edited 3D object Beside that, we also can change texture of the object. Figure 14 show how the 3D wire frame objects we transform into the solid texture, Figure 15 texture the object using the generated texture and Figure 16 show the 3D objects with the real texture. Figure 14: 3D objects with solid texture

11 Figure 15: 3D objects with generated texture 3.9 Query of objects in Bentley Map Figure 16: 3D objects with real texture There is a possibility to query spatial objects stored in Oracle database via Bentley Map. The linkage between the two systems i.e. Oracle Spatial and Bentley Map needs to be setup first to perform spatial queries. In the experiment, the registrations of spatial objects are conducted using two methods, i.e. registration by faces and using multi polygons. Therefore, the query from each method will be highlighted. In Bentley Map, the query is conducted via the visual SQL Query Builder features. Figure 17 shows the list of spatial attributes based on the selected table. The query for faces registration is conducted by

12 selecting the faces attributes. The output of the experiment can be seen in figure 18. The same method is also applied for querying multi polygon registration. Figure 19 shows the result of the query. Figure 17: Visual SQL Query Builder (with list of spatial attributes) Figure 18: The result of the spatial query based on face-by-face method

13 Figure 19: The result of the spatial query based on multi polygon method 4.0 CONCLUDING AND REMARKS In this paper, we have discussed how to manage 3D spatial objects on Oracle Spatial 10g and visualize in Bentley Map and exhibited valuable information related to 3D functionality (query based on 3D objects selection, editing 3D spatial objects and attributes) currently offered. In addition visualising 3D objects stored in a DBMS is not always straightforward. With Bentley Map it is possible to visualise 3D objects rather easily, however the posting of data to the DBMS is not straight forward. The user is expected to have excellent skills in both systems, i.e. understanding the conceptual representation in Bentley Map and being aware of the implementation in storing geometrical and topological data in Oracle Spatial 10g. In the future, we would like to extend the work by addressing the automated spatial data updating and maintenance. ACKNOWLEDGEMENTS We would like to thank to Mr. Beh Boon Heng from Bentley System Malaysia for their assistants on Bentley product and to the Ministry of Science, Technology and Innovations (MOSTI) as well as Universiti Teknologi Malaysia (UTM) for the research funding. REFERENCES Arens, C., J.E. Stoter, and P.J.M. van Oosterom (2003), Modelling 3D spatial objects in a GeoDBMS using a 3D primitive, under review for AGILE Batty M, Chapman D, Evans S, Haklay Mi, Kueppers S, Shiode N, Smith A, Torrens P, M, 2000, Visualizing the city: Communicating Urban Design to Planners and Decision-Makers, ISSN: , CASA, UCL, Batty M, Dodge M, Jiang B, Smith A, 1998, GIS and Urban Design, ISSN: CASA, UCL, Bentley (2002), Bentley Map edition (2007). URL: De La Losa, 1998, Toward a 3D GIS: Conception of a 3D GIS with a complete topological management, In: Proceedings of GIS PlaNET 98 Conference, Lisbon, Portugal ESRI, 1997, Using ArcView 3D Analyst. ESRI Publication, Redlands, California, USA, 118. p.

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